302 



LOUIS PASTEUR 



cause the yeast sown is immediately held in check by a 

 development of anaerobian vibrios. For greater security, we 

 may add to the fermentable liquid, at the moment when it 

 is prepared, a very small quantity of tartaric acid, which 

 will prevent the development of butyric vibrios. 



The variation of the ratio between the weight of the 

 yeast and that of the sugar decomposed by it now claims 



special attention. Side by side 

 with the experiments which we 

 have just described, we con- 

 ducted a third lot by means of 

 the flask C (Fie. 4), holding 4.7 

 litres (Sy 2 pints), and fitted up 

 like the usual two-necked flasks, 

 with the object of freeing the 

 fermentable liquid from foreign 

 germs, by boiling it to begin 

 with, so that we might carry on 

 our work under conditions of 

 purity. The volume of yeast- 

 water (containing 5 per cent, of 

 sugar) was only 200 cc. (7 fl. 

 oz.), and consequently, taking in- 

 to account the capacity of the 



flask, it formed but a very thin layer at the bottom. On 

 the day after impregnation the deposit of yeast was already 

 considerable, and forty-eight hours afterwards the fer- 

 mentation was completed. On the third day we collected 

 the yeast after having analyzed the gas contained in 

 the flask. This analysis was easily accomplished by plac- 

 ing the flask in a hot-water bath, whilst the end of the 

 curved tube was plunged under a cylinder of mercury. The 

 gas contained 41.4 per cent, of carbonic acid, and, after the 

 absorption, the remaining air contained: 





FIG. 4 



Taking into consideration the volume of this flask, this 

 shows a minimum of 50 cc. (3.05 cub. in.) of oxygen to 



bis 



,. 



